Aircraft engine starting, hard starting aircraft engines, problems starting Rotax aircraft engines.

The hard starting problem can be traced to engines using an A or B reduction drive with over 150 hours on them. The spring washers inside the gear box loose their tension. This causes a back lash which prevents the engine from starting, or allows it to start but prevents it from coming off an idle.

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The next most often diagnosed problem is the electric starting system. I say system  because for the electric start to work properly needs

1. too be in good working order
2. have cables that supply it power of the right thickness of wire
3. have a battery that provides enough voltage and high cranking power
4. uses the proper and working regulator rectifier

The electric starter like any other part of the plane needs regular service, which may include replacement of brushers. If the plane is store outside it is recommended that the rubber breather boot face DOWN to prevent UV deterioration to the boot and stop water from entering the starter motor.

The cables providing power to the starter, AND ground to the engine and battery must be as short as possible and be large enough gauge wire for the least possible resistance and minimum voltage loss.

NOTE: most engines are RUBBER mounted - thus a separate ground cable is required running from the battery DIRECTLY to the starter, to provide an adequate ground for the starter to work.

The battery used should be 18 to 21 amp hours in strength and be the kind that provides high cranking power. The Rotax CDI engines require a minimum of 600 RPM to produce enough spark to start the engine.

Regulator -  Rectifiers

Rotax Engines have built in generating systems that put out current that is converted by the regulator - rectifier to DC current. The output is usually 13.5 volts.  However if the wrong regulator rectifier is used the engine can produce well in excess of this at higher rpms.

This overcharges or "boils" the battery which over a period of time will cause it to fail. It also causes considerable "static" interference in radios and audio equipment.

Many type of regulator rectifiers also allow voltage to "leak" from the battery. Over a period of time this can cause the battery to loose it's cranking power, or drain completely. A simple solution to this is to connect the positive output of the regulator rectifier to the side of the ignition switch that has power only when the ignition switch is turned on, thus isolating it from the battery.

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Fuel tank location

In many cases the fuel tank is located a considerable distance from the engine. Some fuel tanks are located below the engine. This can lead to hard starting because the fuel has be first pumped up into the carbs.

In these cases it is suggested that a primer system be used to help bring fuel into the carb bowls. A simple primer bulb or an electric fuel pump connected in a parallel system can be used to bring the fuel quickly into the carb bowls.

Ignition system - Rotax engines now use a dual CDI ignition system. This system is very reliable but requires about 600 rpm to provide enough spark to start the engine. For best spark the spark plugs must be in good working order, set to factory specs for YOUR ENGINE make and model, the air gap between the magneto generator and ignition pick up's checked.

I areas where humidity and condensation are present it is suggested that the pickups be squirted occasionally with WD 40 to help keep moisture off them.

Ultralight Aircraft News.ca Magazine
Canada
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